The objective of this proposal is to investigate: A. the way in which cell mediated and humoral responses to TRA (Tumor Rejection Antigens) demonstrable in vitro relate to tumor status in vivo in a chemically induced rat colo-rectal tumor model - an animal model which possibly reflects situations in humans bearing colon carcinoma; B. a basis for immunotherapy trials in colo-rectal tumors in a rat model by studying the effects of combined immune manipulation by non-specific immune potentiators and specific unblocking therapy both on antitumor immune response in vitro and tumor status in vivo. We will use in vitro techniques based on target cell - effector cell interaction, i.e. microcytotoxicity test and macrophage (leukocyte) migration inhibition test to study the antitumor immune response in vitro.